1. Field of the Invention
The present invention relates to wireless tire pressure monitoring system (TPMS) sensors and more particularly to such sensors which have an external aerial for achieving wireless communication with a receiver unit.
2. The Prior Art
Wireless sensors are well known for use in tire pressure monitoring systems, the sensor being located within the inflation area of a wheel/tire assembly so as to be exposed to the pressurised fluid contained therein and then communicating wirelessly, such as by R/F communication, with a receiver located remotely from the wheel, such as in the wheel arch. In order, then, to achieve the necessary communication, the sensor must include some sort of antenna for broadcasting and receiving signals. In some designs, the antenna is enclosed within the sensor housing, but for some applications, this arrangement has been found not be produce acceptable results and instead an external aerial is provided on the sensor which typically extends away from the sensor into the space formed between the wheel and tire when inflated. However, this presents problems when a tire is being fitted to a wheel. As the bead of the tire is moved across the outer surface of the wheel during fitting, it can engage the antenna unless care is taken by the fitter, resulting in damage to the aerial and hence reducing the range of the sensor or even preventing wireless communication altogether.